The use of plastic containers is continuing to grow at a rapid rate. In many marketing areas, such as in marketing of liquid or semi-liquid (viscous) cosmetics and related products, the plastic container is by far the container of choice. The plastic container, such as a bottle or jar, is not only non-breakable but can be molded so as to be more attractive than other containers. Attractive surface textures and embossed designs can easily be included as the container is formed. In addition, from a cost standpoint, plastic is very competitive with the other materials used for containers. One of the most popular containers for the marketing of cosmetic products, as well as other liquid, semi-liquid and cream products, is a blow molded container of a clear plastic, such as polyethylene terephthalate (PET).
The most common approach for forming such containers is by straight blow molding of a parison in a mold. In the past, some smaller containers have been formed by straight injection molding, but in this case the shape of the container leaves much to be desired. For example, in a typical injection molding operation, the inherent mold taper and characteristic sink of the body side walls leaves the container with a somewhat distorted look. For this reason, the blow molding is the most popular process, with of course the parison for the blow molding operation being formed by injection molding. A typical approach for straight blow molding with the parison being formed by injection molding is illustrated in the Nishikawa et al. U.S. Pat. No. 4,164,298, issued Aug. 14, 1979. As set forth in this patent and others, this approach is to provide a relatively large container from a relatively small parison. As a result of the blow molding, the body side wall and the bottom are substantially stretched and are relatively thin. The entire container is formed from a single tubular parison (see FIG. 4 of the '298 patent).
In the approach taught by the '298 patent, the technique leaves much to be desired where an annular rim on the bottom of the container is desired. For example, as shown in FIG. 1, according to these prior art teachings, there is necessarily a hollow ring formed in the annular rim (see rim 3). Furthermore, the body of the container is very thin and this provides difficulty in handling due to the tendency of the side wall to collapse when squeezed or simply picked-up for use.
On the other hand, containers that are injection molded do not suffer these problems since the size of the molding cavity determines the thickness of all parts, including the side wall of the body. While others that have recognized this benefit have tried to solve the problem of mold taper and sink when injection molding so far it has not been accomplished. Especially for certain containers, such as bottles or jars for cosmetic products, there is thus a need for combining the best concepts of injection molding and blow molding into a single inventive approach wherein the finished container retains the favorable characteristics of both an injection molded and a blow molded container. That is, a container that can be made with a body having a strong and stable body and side wall, and an equally strong bottom wall and enlarged annular corner portion. The corner portion should also be free of the characteristic hollow ring that typically results from a straight blow molding operation.